Athens, Greece to Barcelona is an approximately 6.5-hour flight. You can also take a bus; or drive. You'll gain 1 hour traveling from Athens to Barcelona due to the time zone difference. Traveling from Athens in June, expect nights in Barcelona to be about the same, around 22°C, while days are slightly colder, around 30°C. Wrap up your sightseeing on the 4th (Wed) early enough to travel back home.